A conventional bicycle seat is connected with a seat post which is inserted in the seat tube of the bicycle frame, and the seat is secured by a clamp unit. The seat supports the cyclist's weight and bears the force transmitted from the ground. The latest version of the bicycle seats can adjust the height and angle of the seat.
The conventional seat adjustable devices generally include mechanical adjustable devices, hydraulic/pneumatic adjustable devices, and hybrid adjustable devices which uses air and hydraulic media. The mechanical adjustable devices use mechanical parts to set the relative height between the seat post and the seat tube by linear movement. The hydraulic/pneumatic adjustable devices use hydraulic liquid such as oil or air cooperated with paths to achieve the purposes of adjustment of the seat. The hybrid adjustable devices utilize both of the air and hydraulic liquid to adjust the pressure change between the oil room and the air room to adjust the height of the seat relative to the seat tube.
The hydraulic/pneumatic adjustable devices include an outer tube and a seat post, and oil rooms and air rooms located in the outer tube and the seat post. There are two oil rooms and oil paths communicate between the oil rooms. Valve units are located in the pre-set positions of the oil paths so as to adjust the volume of the oil. The related positions between the parts of different hydraulic/pneumatic adjustable devices are different.
Taiwan Utility Model 099221791 discloses a hybrid adjustable device which has an outer tube, an inner tube, a head unit and an adjustable unit, wherein the inner tube is received in the outer tube and movable relative to the outer tube. The head unit is connected to an end of the inner tube which extends out from the outer tube. The adjustable unit is connected to the head and the inner tube and includes a path, an interior tube that is fixed to the head unit and has one end inserted into the inner tube, a shaft extending through the interior tube, a fixing member fixed to the distal end of the interior tube and located in the inner tube, a piston movably mounted to the inner tube and movable relative to the fixing member, a valve unit connected to the head unit and a handle that is pivotably connected to the head unit and co-rotated with the shaft. The inner tube defines a sub oil room between the piston and the fixing member, and a main oil room is defined between the fixing member and the distal end of the inner tube. The path is located in the inner tube, the interior tube and the fixing member. An air room is defined between the piston and the head unit. By operation of the handle, the shaft opens or closes the path so that the oil flows through the path to move the piston relative to the fixing member, and in the meanwhile, changes the volume of the oil in the main oil room and the sub oil room, and compresses the air in the air room.
Another hybrid adjustable device is disclosed in Taiwan Utility Model 098209833 and includes a seat post, a seat tube in which the seat post is linearly movable, a connection portion connected to the top of the seat tube and having a through hole, a head unit connected to the top of the seat tube so as to clamp the seat, a height adjustable device located between the head tune and the seat tube so as to adjust the linear movement of the seat tube and the seat post. The height adjustable device has a adjustable path which communicates with the through hole. By control of the close and open statuses of the adjustable path, the seat post is movable linearly in the seat tube and set its position. A pressure balance device is connected to the connection portion to assist the regulation of the oil and has a bottle with a piston received therein. The piston defines the interior of the bottle into an oil room and an air room. An oil path is defined in the bottle and communicates with the oil room and the through hole.
The first embodiment of the prior art shows an inner tube movably inserted into the outer tube with oil and air located therein and the users can control the positions of the oil in the inner and outer tube, and control the pressure of the air. The handle is exposed from the seat tube and no exterior oil bottle is needed. The second embodiment of the prior art discloses a pressure balance device which is located outside of the seat tube, by control to the adjustable path, the seat post is movable linearly relative to the seat tube to adjust the height of the seat.
When the seat is adjusted to a lower position, the seat post has to be merged into the seat tube and this compresses the room of the oil room so that the oil in the oil room has to move to other space to be storage. When the seat is adjusted to a higher position, the oil flows back to the oil room. Therefore, there is a sub oil room for storage of the oil.
The sub oil room of the first embodiment is located in the seat tube so that the size of the seat tube has to be large enough to accommodate the oil, therefore, the seat tube and the outer tube have to be made in special specifications. The size of the bicycle frame is increased as well to cooperate with the large sized seat tube. The exterior bottle of the second embodiment does not need to enlarge the size of the seat tube so that the conventional bicycle frame can be used. However, the cyclists may hit the exterior bottle during cycling. The exterior bottle does not meet the aesthetic expectation. The exterior bottle has to be made individually and the installation takes time which increases the manufacturing cost.
The present invention intends to provide a height adjustable bicycle seat tube which does not need the exterior bottle and has low manufacturing cost.